Submitted on November 9, 2006
Accepted on September 4, 2007
Microtubule dynamics and Rac1 signaling independently regulate barrier function in lung epithelial cells
Magdalena J. Lorenowicz1, Mar Fernandez-Borja2, Anne-Marieke D. van Stalborch1, Marian AJA van Sterkenburg3, Pieter S. Hiemstra3, and Peter L. Hordijk1*
1 MCB, Sanquin Research, Amsterdam, Netherlands
2 MCB, Sanquin Research, amsterdam, Netherlands
3 Pulmonology, LUMC, Leiden, Netherlands
* To whom correspondence should be addressed. E-mail: p.hordijk{at}sanquin.nl.
Cadherin-mediated cell-cell adhesion controls the morphology and function of epithelial cells and is a critical component of the pathology of chronic inflammatory disorders. Dynamic interactions between cadherins and the actin cytoskeleton are required for stable cell-cell contact. Besides actin, also microtubules target intercellular, cadherin-based junctions and contribute to their formation and stability. Here, we studied the role of microtubules in conjunction with Rho-like GTPases in the regulation of lung epithelial barrier function using real-time monitoring of transepithelial electrical resistance. Unexpectedly, we found that disruption of microtubules promotes epithelial cell-cell adhesion. This increase in epithelial barrier function is accompanied by the accumulation of 
-catenin at cell-cell junctions, as detected by immunofluorescence. Moreover, we found that the increase in cell-cell contact, induced by microtubule depolymerization, requires signaling through a RhoA/Rho kinase pathway. The Rac1 GTPase counteracts this pathway, because inhibition of Rac1 signaling rapidly promotes epithelial barrier function, in a microtubule- and RhoA-independent fashion. Together, our data suggest that microtubule-RhoA-mediated signaling and Rac1 control lung epithelial integrity through counteracting, independent pathways.
